1. Field of the Invention
The present invention concerns the conversion of digital data into bit-map mode.
2. Description of the Related Art
In a computer, an electronic document includes a collection of objects such as text, image or vectorised drawing (that is to say a set of geometric figures).
In order to be able to print this document, it is necessary to translate it into a representation which can be interpreted by the printer. For example, an inkjet printer processes information of the array of dots type, each dot containing the information for distributing ink at a precise coordinate of the printing medium, such as a sheet of paper. The concern here is therefore with the conversion of a document into bit-map mode, so that it becomes possible for the document to be interpreted for the printer.
A printer generally prints a document band by band, a band corresponding to the width of the print head.
Moreover, it is known that the array of dots obtained can be compressed for the purpose of reducing the transmission time and pass band required between the computer and the printer.
The patent application Ser. No. 99/02303 filed by the applicant presents a compression technique in which a digital signal is decomposed into signals of frequency sub-bands, this decomposition being effected by blocks of samples.
The document U.S. Pat. No. 5,638,498 presents a technique of conversion into bit-map mode in which the data are processed by blocks.
In this context, the invention aims to provide a method and device or conversion into bit-map mode which allows processing by band, whilst minimising the memory size necessary for storing the data in the course of processing.
To this end, the invention proposes a method of converting, into bit-map mode, digital data representing physical quantities, in order to transmit the converted data from a first data processing device to a second data processing device, including the steps of:
forming bands of data to be converted, the bands having a predetermined height,
forming blocks in each band previously formed, characterised in that
the blocks have a first block size parameter which is determined according to at least one characteristic of the first device.
The invention also relates to a method of converting, into bit-map mode, digital data representing physical quantities, in order to transmit the converted data from a first data processing device to a second data processing device, including the steps of:
forming bands of data to be converted, the bands having a predetermined height,
forming blocks in each band previously formed, characterised in that
the blocks have a second block size parameter which is determined according to at least one characteristic of the second device.
The invention concerns a method which combines the characteristics of the two methods presented above.
Correlatively, the invention concerns a device for converting into bit-map mode digital data representing physical quantities, in order to transmit the converted data to a second data processing device, having:
means of forming bands to be converted, the bands having a redetermined height,
means of forming blocks in each previously formed band,
characterised in that the block formation means are adapted to form the blocks so that:
the blocks have a first block size parameter which is determined according to at least one characteristic of the first device.
The invention also relates to a device for converting into bit-map mode digital data representing physical quantities, in order to transmit the converted data to a second data processing device, having:
means of forming bands to be converted, the bands having a predetermined height,
means of forming blocks in each previously formed band,
characterised in that the block formation means are adapted to form the blocks so that:
the blocks have a second block size parameter which is determined according to at least one characteristic of the second device.
The invention also concerns a device which combines the characteristics of the devices presented above.
By virtue of the invention, the memory size necessary for storing the data in the course of processing during their conversion into bit-map mode and their compression is reduced, whilst preserving a good quality of reproduction of the printed document.
According to preferred characteristics, which may be combined:
the first parameter is a block height,
the at least one first characteristic is the memory available in the first device,
the second parameter is a block width,
the at least one second characteristic is the memory available in the second device.
These characteristics allow a simple and economical implementation of the invention.
According to a preferred characteristic, the second device is a printer and the band height is determined according to the size of the print head of the printer.
According to another preferred characteristic, the blocks overlap in pairs over a predetermined overlap width, preferably equal to one sample. The overlap makes it possible to retrieve the data without loss, and the overlap of a sample is a minimum overlap which minimises the memory occupation of the data.
According to another preferred characteristic, the block width is determined so that the product of the band height and the block width minus the overlap width does not exceed the memory size available in the printer.
According to another preferred characteristic, the block height is determined so that the product of the block height, minus the overlap width, and the block width, also minus the overlap width, does not exceed the memory size available in the computer.
According to another preferred characteristic, the block height is determined so that the band height is an integer multiple of the block height.
The above block size characteristics make it possible to adapt the conversion into bit-map mode to the performance of the devices used.
According to another preferred characteristic, the data are processed band by band, and then in each band the data are processed block by block, and the blocks are processed so that:
the blocks are processed column by column,
the blocks in any column are all processed before passing to another column,
the columns of blocks are processed in the order of their printing by the print head.
The order of processing of the blocks optimises the memory occupation of the data in the course of processing.
According to another preferred characteristic, the method includes the steps of:
translation of each block into frequency sub-bands,
quantisation of the samples of the frequency sub-bands, and
entropic coding of the quantised samples.
Thus the data converted into bit-map mode are compressed before being transmitted to the printer.
The device has means of implementing the characteristics disclosed above.
The invention also concerns a digital apparatus including the device or means of implementing the method.
The invention also concerns a system including the previously disclosed device connected to a printer.
The advantages of the device, of the digital apparatus and of the system are identical to those previously disclosed.
The invention also concerns an information storage means which can be read by a computer or by a microprocessor, integrated or not into the device, possibly removable, and stores a program implementing the method disclosed above.
The invention also concerns a computer program product comprising instructions for implementing the method disclosed above.